The present invention relates to a photosensitive composition and a photosensitive laminate, and more particularly to a photosensitive composition and a photosensitive laminate which are developable by an aqueous alkali solution.
A photoresist formed from a photosensitive composition has been employed in the preparation of printed circuit boards. Conventionally, a photoresist image has been produced by coating a liquid photosensitive composition containing a solvent to a board for printed circuit boards, drying the coating to remove the solvent, exposing imagewise the dried coating to an active light and developing the image.
In recent years, in order to improve the workability, air pollution and yield of the above process, there has been proposed and employed availably a flexible three layer laminate, i.e. a photosensitive laminate (hereinafter referred to as "photosensitive element") composed of a film support, a dried layer of a photosensitive composition (hereinafter referred to as "photosensitive layer") and a protective cover film. As a photosensitive composition, there are known the so-called alkali development type that unexposed areas are removed by an aqueous solution of an alkali and the so-called solvent development type that unexposed areas are removed by an organic solvent.
In case of a photosensitive element of the alkali development type, a protective cover film is removed from the element and the photosensitive layer supported on a film support is then adhered under pressure with heating to the surface of a board. The photosensitive layer is then exposed imagewise to light through a negative film, and after peeling off the support film, the unexposed areas are removed with an aqueous alkali solution as a developer to form a photoresist image. Etching or plating treatment of the metal surface of the board is carried out by employing the thus formed resist image as a photomask, and the photoresist image was then removed from the metal surface by employing an aqueous stronger alkaline solution than the developer to provide a printed circuit board or the like.
It is necessary that the photoresist image is sufficiently resistant to the etching or plating treatment of the board. In the etching treatment, a metal (usually copper) of the surface area of the board is removed by employing an aqueous solution of ferric chloride, cupric chloride or ammonium persulfate. Many kinds of the plating liquids are known, and for instance, in case of a photosensitive element of the alkali development type, acidic plating liquids are usually employed. The metal surface in the area not masked with the photoresist image is plated by solder plating or a combination of copper sulfate plating and solder plating. In the plating treatment, an electric current is passed through a highly concentrated solution of a chemical reagent, and accordingly the plating treatment is severer than the etching treatment.
Photosensitive elements of the alkali development type are disclosed, for instance, in Japanese Unexamined Patent Publication (Tokkyo Kokoku) No. 94388/1977, No. 130701/1977, No. 128688/1978 and No. 147323/1975. However, these conventional photosensitive elements of the alkali development type have the disadvantage that the photoresist image obtained therefrom is insufficient in the electroplating resistance. That is to say, though the photoresist image is endurable to the electroplating with a copper sulfate plating liquid and a solder plating liquid having a low concentration of borofluoric acid, it is poor in resistance to a solder plating liquid for common use having a borofluoric acid concentration of more than 350 g./liter, and in the plating with such a solder plating liquid, peeling, blister and deposition of solder in the interface between the resist and the board occur. The concentration of borofluoric acid in the solder plating liquid which is the most commonly used is from 350 to 500 g./liter, and within this range, the plating liquid for obtaining eutectic crystal solder of dense particles can be stably controlled.
It is an object of the present invention to provide a photosensitive composition capable of forming a photosensitive layer of alkali developable photosensitive elements having an excellent plating resistance, good etching resistance, chemical resistance and other properties required for the alkali developable photosensitive elements such as an adhesive property to boards and a developing property.
Another object of the invention is to provide an alkali developable photosensitive element having an excellent plating resistance and moreover having good etching resistance, chemical resistance, adhesive property to boards and developing property.
These and other objects of the present invention will become apparent from the description hereinafter.